How much you earn is dependent on how much interest you charge. It is pretty much self explanatory and only needed a simple mathematics to calculate the diffrence (profit) between the ininital loan that you will grant and the payable amount with interest.



It is advisable to ask collateral since you do not know the person who will ask  for a loan here in the forum.  But some old lender had given and exemption to the account that is enrolled in signature campaign paid weekly in BTC.



You can start by planning and creating terms and compare them to the existing lending service here: https://bitcointalk.org/index.php?board=65.0.  Of course borrower likes smaller interest so try to think of a competitive interest that can entice borrower to taking your service.

Also, please take not of many scammers that will take advantage of your service.  Many had been recorded that after borrowing huge amount of money, the defaulted on the loan and abandon the account they used for borrowing.